In prior-art, fuel-operated heater, the combustion of fuel, usually gasoline or diesel fuel, takes place in the combustion chamber under air excess. This means that oxygen is still present in the waste gas and stoichiometrically complete combustion does not take place. The range of operation of the combustion chamber covers, in terms of combustion engineering, a lambda range (possible air-to-fuel ratios within the range of operation). To ensure the operation of the device in this range, the amount of combustion air is set during the installation of a prior-art heater or of the fan by means of a variable bypass opening, or the amount of fuel is set in the case of a fuel feed pump by means of an adjusting screw. This requires a high design effort for the heater and long adjusting times.
The above-mentioned range of operation may be left during the operation of a heater for the following reasons:
Clogging of the combustion air intake or of the waste gas outlet, as a result of which the amount of combustion air is reduced. PA1 Clogging of a heat exchanger connected to the heater by combustion residues, as a result of which the amount of combustion air is also reduced during the operation. PA1 Change in the mass flow of combustion air during the operation of the heater at different altitudes above mean sea level.
If the range of operation or lambda range is left, the combustion values deteriorate. The heater no longer operates satisfactorily and it may fail.